1. Field of the Invention
The present invention relates to an image forming apparatus and more particularly to an image forming apparatus including two power supply lines for insuring safety in the event of a hazardous error and automatically restoring original conditions after recovery from the error.
2. Description of the Background Art
A facsimile apparatus, copier, copier, printer or similar electrophotographic image forming apparatus, for example, includes a fixing unit that fixes a toner image formed on a sheet with heat. More specifically, a latent image is formed on a photoconductive element by a light beam modulated in accordance with image data and then developed by toner. The resulting toner image is transferred from the photoconductive element to a sheet. A heat roller fixes the toner image on the sheet with heat generated by a heater accommodated in the heat roller.
The heater heating the heat roller is controlled to preselected temperature while being protected from overheating. For this purpose, a thermistor, for example, senses the temperature of the heater while sending its output to a controller. The controller ON/OFF controls the heater in accordance with the output of the thermistor to thereby maintain the heater at preselected temperature.
To meet the increasing demand for energy saving, Japanese Patent Laid-Open Publication No. 8-251317, for example, discloses an image forming apparatus configured to reduce power consumption when a power supply is turned off. On the other hand, Japanese Patent Laid-Open Publication No. 2000-289885, for example, teaches an image forming apparatus implemented as a multifunction printer including two power supply lines. If the power supply of a multifunction printer is fully turned off, then the printer cannot receive print data from, e.g., a personal computer or prevents its weekly timer from operating. In light of this, even when the power supply is turned off, the two power supply lines continuously energize part of control sections with a minimum of power and causes, on the generation or a print request or similar request, such a control section to start the entire printer system. This successfully enhances efficient manual operation while saving power.
It is a common practice with an image forming apparatus to cope with, e.g., the runaway of a CPU (Central Processing Unit) or controller by protecting a heater from overheating with a temperature fuse or a thermostat or with an analog comparator. However, this kind of scheme is not a drastic measure for protecting the image forming apparatus in the event of the runaway of the controller or similar critical error. For example, the image forming apparatus is apt to start a fire when a drive motor does not stop rotating, when the heater does not turn off due to the runaway of the CPU or when a high-tension output does not stop. In such a case, even when the CPU is reset, the high-tension output is likely to again turn on. Moreover, when the CPU is reset, all modes set beforehand are deleted and must be set all over again, resulting in inefficient manual operation.
It is an object of the present invention to provide an image forming apparatus capable of surely turning off power supplies assigned to a charging section and a drive section when critical errors, which are apt to bring about a fire or similar danger, occur in such power supplies, thereby enhancing safety.
It is another object of the present invention to provide an image forming apparatus capable of shutting off power supply when any failure considered to be particularly dangerous occurs, thereby further enhancing efficient operation.
It is a further object of the present invention to provide an image forming apparatus capable of adequately coping with a fire or similar hazardous error to thereby further enhance safety.
An image forming apparatus of the present invention includes a main controller for controlling various sections included in a signal system and an engine controller for controlling various sections included in a load system. A first power supply applies power to the main control means while a second power supply applies power to the engine control means. A first establishing/interrupting device selectively establishes or interrupts the application of power to the second power supply in response to the output of the first power supply. When an error occurs in any one of the sections of the load system, the engine controller sends to the main controller status information representative of original conditions set up before the error and error information representative of the error. On receiving the status information and error information, the main controller stores the status information in its memory and causes the first establishing/interrupting device to interrupt the application of power to the second power supply, thereby interrupting the application of power to the load system.